() i screenshot the question and choices d:

Ah, looks like a special right triangle to me, just got done learning about these.

Alright, so, since this is a 30-60-90 triangle, 6 is the smallest leg (as across from 30 degree is the smallest leg), labeled as s. Across from the 90 is 12, as that is 2s.

The missing side, across from the sixty, would be 6 square root of 3 (fourth answer).

The easiest way to do this would be to implement the Pythagorean Theorem (a squared + b squared = c squared) so 6 squared + x squared = 12 squared.
Then you would have 36 + x squared = 144.
Subtract the 36 from both sides, then you'll have x squared = 108. take the square root of each side, and you have x= the square root of 108, which simplifies to 6× the square root of 3. So, X=6√3

10.4 is the answer for you